package day01_07.day06;

import java.util.Scanner;

public class Main01 {
    public static void main(String[] args) {
        Scanner scn = new Scanner(System.in);
        int W = scn.nextInt();
        int H = scn.nextInt();
        int[][] array = new int[W][H];


        int num = 0;
        for (int i = 0; i < W; i++) {
            for (int j = 0; j < H; j++) {
                if (array[i][j] == 0){
                    num ++;
                    //只有在此处放值时，他身边两个元素才不能放
                    if (i + 2 < W){
                        array[i + 2][j] = 1;
                    }
                    if (j + 2 < H){
                        array[i][j + 1] = 1;
                    }
                }

            }
        }
        System.out.println(num);

    }


}
